(a) Technical Field
The present invention relates to a control system and method for a hybrid vehicle, and more particularly, to a system and method of controlling a vehicle employing a parallel type hybrid power train in which a motor is mounted to a side of a transmission.
(b) Background Art
In a parallel hybrid vehicle utilizing a transmission mounted electric device (TMED), an engine, an engine clutch, a motor, and a transmission are sequentially connected to each other such that both an electric vehicle (EV) mode (i.e. powered only by the motor) and a hybrid electric vehicle (HEV) mode (i.e. powered by the engine and the motor) are allowed by controlling the engine clutch.
A vehicle employing such a parallel type hybrid power train is driven only by the motor by releasing the engine clutch while manipulating an acceleration pedal to a small extent (“slight”). The vehicle is driven by driving forces of the engine and the motor by coupling the engine clutch while manipulating the acceleration pedal to a large extent (“deep”).
If the driver initially works the acceleration pedal slightly to increase the speed to a predetermined speed using the motor, and then works the acceleration pedal deep, an RPM of the engine and an RPM of the motor are synchronized to solve an impact of the vehicle due to a coupling of the engine clutch, and then the engine clutch is coupled to transfer a torque of the engine to the engine clutch.
If the driver works the acceleration pedal deep, then the vehicle needs to be accelerated even while the RPM of the engine and the RPM of the motor are synchronized. As a result, the motor is driven to a maximum torque. However, if it takes a long time to synchronize the engine and the motor, then the engine clutch is not coupled before the synchronization, the power of the engine is not transferred, and only the motor is driven. This results in a large consumption of the state of charge (SOC) of a battery and results in an inferior fuel ratio.
FIG. 1 corresponds to a method of controlling a hybrid vehicle according to the related art. If an RPM of a motor is higher than an RPM of an engine when an operator works an acceleration pedal deep during an EV mode, and thus a torque higher than a maximum torque of a motor is necessary, then a speed of the engine is controlled to be synchronized with the RPM of the motor so that a synchronous clutch coupling (S510) for coupling of the engine clutch is performed. If the RPM of the motor is lower than the RPM of the engine, then a slip clutch coupling (S520) is performed in which the engine clutch is synchronized while being slipped and then the clutch is completely coupled after synchronization of the RPMs.
However, during the synchronous clutch coupling (S510), when the RPM of the motor increases rapidly so as to reduce the RPM of the engine, the vehicle is driven only by a motor at a maximum output. This excessively consumes an SOC and deteriorates the fuel ratio while also causing the engine to consume fuel through an unnecessary speed control.
This phenomenon occurs because an RPM increment by which an increase of speed of the motor cannot be pursued even when the speed is controlled to a maximum is generated in the engine consuming a fossil fuel.
The items described in the background art are provided just to help understanding of the background of the present invention, and shall not be construed to admit that they correspond to the technologies already known to those skilled in the art to which the present invention pertains.